1. Field of the Invention
The present invention relates to compositions and methods for pain relief.
2. Description of the Related Art
Pain results from the noxious stimulation of nerve endings. Nociceptive pain is caused by stimulation of nociceptors (e.g., a needle stick or skin pinch), which then transmit impulses over neural pathways to the spinal neurons and then to the brain. Neuropathic pain is caused by damage to neural structures, such as peripheral nerve endings or nociceptors, which can generate impulses in the absence of stimulation (e.g., herpes zoster pain after the rash has healed).
In contrast to pain treatment with systemic agents, pain can be treated locally by topically administering a pain relieving agent directly to the painful area to block the nociceptive mechanistic pathway. Local anesthetics prevent the generation and conduction of nociceptive nerve impulses. Thus, for example, a local anesthetic or analgesic can be topically applied at the pain area. Advantages of topical anesthetic or analgesic administration over systemic administration of pain relievers include decrease or preclusion of certain side effects, improved patient compliance, and reversible action (i.e., the action can be reversed by removing the anesthetic from the application site).
A variety of drug classes have anesthetic or analgesic properties and can be administered in topical formulations. Traditional local anesthetics or sodium-channel blockers, such as lidocaine prevent the generation and conduction of nerve impulses by decreasing or preventing the large transient increase in the permeability of excitable membranes to Na+. Other agents with analgesic properties include the non-steroidal anti-inflammatories (“NSAIDs”) and opioids, such as morphine.
It is common practice to provide a topical pain reliever using the well-known NSAID, salicylic acid (aspirin). Aspirin has been used effectively for many years in the medical and scientific community as a pain reliever. Despite its benefits, systemic administration of aspirin has been shown to cause certain side effects in its users, for example stomach irritation and other internal problems associated with ingesting aspirin.
Applying an aspirin solution topically to a user's skin, thereby avoiding the need for a user to ingest aspirin, has been shown to be an effective manner of gaining the benefits of aspirin without the potential side effects. However, there are difficulties associated with the ability to achieve a safe and stable form of a topical pain reliever containing aspirin that will remain in suspension within the solution of the topical pain reliever.
In view of these difficulties, other NSAIDs have been utilized for their anti-inflammatory or analgesic properties. It is an important aspect of any NSAID-based topical pain reliever to permeate the necessary layers of the integument or skin in order to relieve pain without adversely affecting vital internal organs. Accordingly, it is accepted that an effective topical pain reliever should be in the form that dissolves the analgesic agents and transports it to the area of pain where it can then permeate the integument or skin to provide effective relief.
Topical pain relievers have been introduced in the past, but such topical pain relievers have traditionally had problems of maintaining the analgesic in suspension within the solution of the topical pain reliever. Further, topical pain relievers have been known to have a delayed onset of action after they have been applied to the integument or skin. Several reasons may cause such a result, for example the topical pain reliever may not effectively permeate the skin.
Many patients with localized pain due to arthritis, bursitis, sprain or muscle strain, bruises or hematomas cannot tolerate conventional NSAIDS. In addition, topical administration of conventional NSAIDS has been known to be ineffective because only a therapeutically ineffective amount of the drug can penetrate the skin. In addition, indications such as acne, psoriasis and eczema are typically refractory to topical or oral administration of NSAIDS.
In addition, joint pain can often indicate the onset of a condition called osteoarthritis. Osteoarthritis is a degenerative joint disease affecting articular cartilage developing in the fourth and fifth decades of life that was initially believed to be a disease of wear and tear due to mechanical stress on the joints. It is now known that the pathology of osteoarthritis is not entirely mechanical and involves changes in the joint metabolism. Specifically, altered glucosamine metabolism appears to play a key role in the development of osteoarthritis.
An effective treatment of osteoarthritis must address two types of problems: (i) pain, and joint tenderness, swelling and stiffness must be alleviated as an immediate patient's problem; and (ii) the degenerative process must be stopped preferably at its earlier stages. Treatment with anti-rheumatics and NSAIDs has not proven successful. Anti-rheumatics, although quickly effective, were recently shown to impair the very function that physicians were trying to improve, and anti-inflammatory drugs alleviate the pain but do not address the underlying degenerative disorder.
Therefore, what is needed is a topical composition that provides effective pain relief, is stable for long periods of time and provides a long shelf-life, and avoids the disadvantages associated with other topical analgesics or systemically administered drugs. What is further needed is a composition that is effective in treating a wide variety of inflammatory conditions by topical application of the composition.
These advantageous properties are provided by the composition set forth in the description that follows. Further advantages will be apparent from the description, or may be realized by the practice of the invention without undue experimentation.